1. Field of the Invention
This invention relates to a method and associated apparatus for testing internal combustion engines, and more particularly to a method and apparatus for testing fuel pump governors for use on diesel engines.
2. Description of Related Art
Internal combustion diesel engines typically use a fuel delivery pump whose delivery rate is controlled by a governor. Further more, many modern diesel engines use a combined fuel injection pump and governor assembly. Since both the pump and the governor are driven by the engine when the pump/governor is operating on the diesel engine, there is a dynamic interactive (closed loop) relationship between the governor throttle (speed control lever) position and the engine speed. For example, when the throttle lever is moved from one setting, i.e. the idle position, to a second setting, i.e. a position known in the trade as the high idle position, the engine speed in revolutions per minute, (RPM) increases until a balanced point is reached between the engine speed and the governor speed setting.
Testing of governors is needed for the proper operation of the fuel pump and as a consequence the diesel engine. Testing may be necessary both for adjusting a new governor/pump combination to specifications given by an engine manufacturer, and to determine whether a new or repaired governor and associated pump are operating properly.
Testing is presently done on test benches which are designed to drive a pump and associated governor and to measure the fuel volume or quantity delivered by the pump for different preset pump speeds and throttle positions. The test benches typically include a variable speed motor, means to set and read out the motor RPM, means to connect a pump and associated governor on to the test bench and the drive motor, and means to supply fuel to the pump and to measure the fuel quantity or volume delivered by the pump as a quantity of fuel per a predetermined number of pump strokes.
The currently available test benches perform the tests by averaging fuel delivery by the pump at given speeds. However, averaging the fuel delivery can average out instantaneous fluctuations in the delivery which may cause engine speed instability.
Test benches available today simply allow to set the pump and governor rotation at a given RPM speed and adjust the governor for an average fuel delivery at that speed. This situation however does not give performance information indicative of the system operation when mounted on an actual engine, since when the equipment is mounted on the test bench the pump/governor RPM are fixed by the setting of the driving motor on the bench, while when the governor and associated pump are mounted on an actual operating engine, both the governor and pump are driven by the engine and the engine RPM are a function of the pump/governor setting and performance. Fuel delivery fluctuations for any reason, including governor malfunction or improper setting will result in speed changes of the engine and further changes in the governor response. This complex interaction is not tested with today's test equipment.
Additionally throttle lever position has no effect on the injection pump test bench speed as it does when operating on the diesel engine because the current benches set such speed at a fixed rate by the setting on the drive motor.
Current test benches permit idle, high idle, rated speed and other speed adjustments but such adjustments are done by measuring average fuel delivery rather than direct speed settings.
Thus there is still a need for a testing method and apparatus that will permit testing of fuel pump governors in a way that simulates the effect of governor control on engine speed and allow testing governors for full-load speed, peak torque speed, and part throttle speed, as well as other governor parameters such as sensitivity, stability and speed droop.